docs: def _get_vs30star(self, vs30, imt):
          """
          This computes equations 8 and 9 at page 1034
          """
          # compute the v1 value (see eq. 9, page 1034)
          if imt.name == "SA":
              t = imt.period
              if t <= 0.50:
                  v1 = 1500.0
              elif t < 3.0:
                  v1 = np.exp(-0.35 * np.log(t / 0.5) + np.log(1500.))
              else:
                  v1 = 800.0
          elif imt.name == "PGA":
              v1 = 1500.0
          else:
              # This covers the PGV case
              v1 = 1500.0
          # set the vs30 star value (see eq. 8, page 1034)
          vs30_star = np.ones_like(vs30) * vs30
          vs30_star[vs30 >= v1] = v1
          return vs30_star